Production of green hydrated chromium oxide



Patented Aug. 6, 1929.

UNITED STATES PATENT OFFICE.

KURT E. MEYER AND HANS KRZIKALLA, F MANNHEIM, GERKAN'Y, ASIGNORS TO GENERAL AIN'ILINE WORSE KS, INC., 01' NEW YORK, N. Y., A. CORPORATION OF DELAWARE.

PROPUCTION OF GREEN HYDRATED GHROMIUM OXIDE.-

No Drawing. Application filed March 8, 1928, Serial No. 260,238, and in Germany March 15, 1927.

This invention relates to the production of green hydrated chromium oxide.

For the production of brilliant green by,-

drated chromium oxide, use is made in. the art 5 mainly of fusion products prepared by heating salts of hexavalent chromium with a large excess of boric acid. The preparation of these chromium oxides, which are known in commerce under various names, particularly Guignets green, is a. tiresome matter because the dilficultly soluble boric' acid has to be removed from the melt and recovered.

We have now foundthat brilliant reen hydrated chromium oxide can be produced in a sim le manner, without boric acid, by

heating '0 romic acid, or its salts, with reducing agents at'a pressure above atmospheric but below 150 atmospheres, and in the presence of water. According to the conditions emplo ed, this method readily furnishes hydrat chromium oxide with va ing contents of water and consequently of di erent shades.

The chromium oxide with higher water content, which can .also be prepared at lower.

2 temperatures, is usually of a darker green than that with lower water content.

The reducingagent may consist of a great variety of organic or inorganic substances with a reducing action, such, for example, as

hydrogen, hydrocarbons, carbon monoxide,

formates, glycerine, sodium thiosulfate and the like, or mixtures thereof. We have found that it is most referable to work with reduc- P ing agents which are not liable of contaminating the finished products, as may ha pen when employing saw dust or othercar onizable or coal matter. It is therefore most advisable eit r to use organic reducing agents which 0 not belong to. the aforesaid ac group, or to employ inorganic reducin orit may find application, in conjunction with substrate, as paint.

The following examples will further illustrate the nature of the said inventionwhich however is not limited thereto. The parts,

are heated and stirred with 600 parts of Water and 140 parts of sodium formate, for about 10 hours at from 270 to 280 C. in an autoclave. After cooling down to about 90 7 (3., the handsome green hydrated chromium oxideis filtered by suction, washed until neutral and dried. If the reduction be effected at .from 200 to 210, 0., a handsomer and darker chromium oxide green, containing from about 22 to 24 per cent of water, is obtained.

The reaction the equation ena oro sncoon Cr,,O 3Na CO,"+ NaOH H 0. Accordingly, the whole of the sodium'in the initial materials is obtained as a by-product 1n the form of alkali suitable for direct utiliproceeds in accordance with zation. Instead of using sodium formate as the reducing agent, carbon monoxide may be forced into the chromium solution, or other organic reducing agents, such as glycerine and the like may be employed.

Example 2.

342 .parts b weight of crystallized sodium chromate an 600 arts of water, with 25 arts by weight of owers of sulfur as reducing agent, are heated for 10 hours in an autoclave, with stirrers, in such a manner that the pressure gauge registers 40 atmospheres;

After cooling the further treatment proceeds as in Exampl mium oxide is obtained.

e1. A handsome green chro- Sulfur may be replaced by other reducing I agents, such as carbon in the form of lampblack or powdered wood charcoal. Whereas the reduction with flowers of sulfur, according to the above example furnishes Glauber salt as b -product, the reduction with carbon gives so ium carbonate and bicarbonate.

Mixtures of reducing agents may also be employed.

. Emampk 3.

An aqueous solution of about 30 to 40 per cent of potassium chromate is heated to 270 C. in an autoclave fitted with a stirrer and a pressure gauge,whereup0n hydrogen is introduced until the pressure amounts to 110 atmospheres. In accord'ance with the gradual consumption, hydrogen is introduced so that the said pressure is maintained, until the absorption has ceased. After cooling, the insoluble, handsome green hydrated chromium oxide is separated from the resulting caustic soda solution by filtration by suction and washed. The hydrogen may be replaced by a mixture of carbon monoxide and hydrogen, such as water gas or by other reducing gases such as methane, acetylene or the like, or mixtures thereof or mixtures of gases containing the latter.

What we claim is 1. A process for the production of green hydrated chromium oxide which consists in heating a compound of hexavalent chromium in the presence of waterat a pressure above atmospheric pressure but below 150 atmospheres with a reducing agent, other than sulfurous acid.

2. A process for the production of green hydrated chromium oxide which consists in heating a compound of hexavalent chromium in the presence of water at a pressure above atmospheric pressure but below 150 atmos pheres with reducing agents comprising an inorganic constituent, but other than su fur ous acid. i

3. A process for the production of green hydrated chromium oxide which consists in heating an a ueous solution of a ehromate at a pressure a ove atmospheric pressure, but below 150 atmospheres with a reducing agent, but other than sulfurous acid.

4. A process for the production of green hydrated chromium oxide which consists in treating a solution of a compound of hexavalent chromium at a temperature above 200 C. and at a pressure above atmospheric pressure but below 150 atmospheres with a reducing agent, but other than sulfurousacid.

5. A process for the production of green hydra-ted chromium oxide which consists in heating an aqueous solution of a chromate at a pressure above atmospheric pressure, but below 150 atmospheres with sulfur.

In testimony whereof we have hereunto set our hands.

KURT H. MEYER. HANS KRZIKALLA. 

